package org.apache.lucene.store;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/** Abstract base class for input from a file in a {@link Directory}.  A
 * random-access input stream.  Used for all Lucene index input operations.
 * @see Directory
 */
public abstract class IndexInput implements Cloneable {
    private char[] chars; // used by readString()

    /** Reads and returns a single byte.
     * @see IndexOutput#writeByte(byte)
     */
    public abstract byte readByte() throws IOException;

    /** Reads a specified number of bytes into an array at the specified offset.
     * @param b the array to read bytes into
     * @param offset the offset in the array to start storing bytes
     * @param len the number of bytes to read
     * @see IndexOutput#writeBytes(byte[],int)
     */
    public abstract void readBytes(byte[] b, int offset, int len) throws IOException;

    /** Reads four bytes and returns an int.
     * @see IndexOutput#writeInt(int)
     */
    public int readInt() throws IOException {
        return ((readByte() & 0xFF) << 24) | ((readByte() & 0xFF) << 16) | ((readByte() & 0xFF) << 8) | (readByte() & 0xFF);
    }

    /** Reads an int stored in variable-length format.  Reads between one and
     * five bytes.  Smaller values take fewer bytes.  Negative numbers are not
     * supported.
     * @see IndexOutput#writeVInt(int)
     */
    public int readVInt() throws IOException {
        byte b = readByte();
        int i = b & 0x7F;
        for (int shift = 7; (b & 0x80) != 0; shift += 7) {
            b = readByte();
            i |= (b & 0x7F) << shift;
        }
        return i;
    }

    /** Reads eight bytes and returns a long.
     * @see IndexOutput#writeLong(long)
     */
    public long readLong() throws IOException {
        return (((long) readInt()) << 32) | (readInt() & 0xFFFFFFFFL);
    }

    /** Reads a long stored in variable-length format.  Reads between one and
     * nine bytes.  Smaller values take fewer bytes.  Negative numbers are not
     * supported. */
    public long readVLong() throws IOException {
        byte b = readByte();
        long i = b & 0x7F;
        for (int shift = 7; (b & 0x80) != 0; shift += 7) {
            b = readByte();
            i |= (b & 0x7FL) << shift;
        }
        return i;
    }

    /** Reads a string.
     * @see IndexOutput#writeString(String)
     */
    public String readString() throws IOException {
        int length = readVInt();
        if (chars == null || length > chars.length)
            chars = new char[length];
        readChars(chars, 0, length);
        return new String(chars, 0, length);
    }

    /** Reads UTF-8 encoded characters into an array.
     * @param buffer the array to read characters into
     * @param start the offset in the array to start storing characters
     * @param length the number of characters to read
     * @see IndexOutput#writeChars(String,int,int)
     */
    public void readChars(char[] buffer, int start, int length) throws IOException {
        final int end = start + length;
        for (int i = start; i < end; i++) {
            byte b = readByte();
            if ((b & 0x80) == 0)
                buffer[i] = (char) (b & 0x7F);
            else if ((b & 0xE0) != 0xE0) {
                buffer[i] = (char) (((b & 0x1F) << 6) | (readByte() & 0x3F));
            } else
                buffer[i] = (char) (((b & 0x0F) << 12) | ((readByte() & 0x3F) << 6) | (readByte() & 0x3F));
        }
    }

    /** Closes the stream to futher operations. */
    public abstract void close() throws IOException;

    /** Returns the current position in this file, where the next read will
     * occur.
     * @see #seek(long)
     */
    public abstract long getFilePointer();

    /** Sets current position in this file, where the next read will occur.
     * @see #getFilePointer()
     */
    public abstract void seek(long pos) throws IOException;

    /** The number of bytes in the file. */
    public abstract long length();

    /** Returns a clone of this stream.
     *
     * <p>Clones of a stream access the same data, and are positioned at the same
     * point as the stream they were cloned from.
     *
     * <p>Expert: Subclasses must ensure that clones may be positioned at
     * different points in the input from each other and from the stream they
     * were cloned from.
     */
    public Object clone() {
        IndexInput clone = null;
        try {
            clone = (IndexInput) super.clone();
        } catch (CloneNotSupportedException e) {
        }

        clone.chars = null;

        return clone;
    }

}
